| Titre : | Advances in karst groundwater protection strategy using artificial tracer tests analysis and multiattribute vulnerability mapping (EPIK method) |
| Auteurs : | Doerfliger, Nathalie, Auteur ; Université de Neuchâtel (CHE). Faculté des Sciences, Auteur |
| Type de document : | thèse/mémoire |
| Année de publication : | 1996 |
| Format : | 308 p. |
| Langues : | = Anglais |
| Mots-clés : | GROUNDWATER PROTECTION ; KARST AQUIFERS ; ARTIFICIAL TRACER TESTS ; INPUT-RESPONSE MODEL ; TRANSFER FUNCTIONS ; PARAMETRIC CONCEPTUAL MODEL ; VULNERABILITY ; MULTIATTRIBUTE OVERLAY METHOD |
| Résumé : |
Karst groundwater protection is a major issue in environmental concern at the end of the 20th century. Karst areas provide large quantities of water for water supply at springs and wells in Europe as well as in Switzerland. Karst environment can be troublesome water sources in certain cases, due either to an accident in a very sensitive area or also to inappropriate protection zones and corresponding regulations.
Karst aquifers are characterized generally by on the one hand, highly heterogeneous structure with the existence of a high hydraulic conductivity karst network more or less connected, developed and surrounded by an important volume of fissured rocks with a low hydraulic conductivity. On the other hand, diffuse and concentrated infiltration with limited filtering and auto-purification action of the contaminants occurs. In matter of karst groundwater protection, therefore, specific strategy has to be developed as required by the Federal Office of the Environment, Forest and Landscape and the dependent Swiss National Hydrological and Geological survey. Two approaches referring to specific conceptual models had been used in the framework of this thesis in order to answer to the following questions on the one hand: does exist a mean transfer function based on artificial tracer tests, that characterizes a given water catchment basin or a part of it and can we use this transfer function to etablish some contaminant predicting scheme in the framework of a hydrogeological impact assessment ? And on the other hand, to suggest an appropriates method to outline the groundwater protection zones of karst water catchment basin, as concentric protection zones are not suitable in karst environment due to its specific hydrological features. Considering the tracing-system (tracing pathway) as an input-response model (black box model) artificial tracer tests are interpreted in terms of transfer functions-impulse response and/or indical response. The transfer function as impulse response is obtained by deconvolution of the tracer breakthrough curve by its corresponding input function. The indical response corresponds to the convolution of the impulse response by a step-unit function. In order to determine mean transfer function to specific parts of a water catchment basin or the whole water catchment basin, a study of variability of the transfer functions by variance and multivariance analyses on the gradients at given percentiles of the indical response and on the modal velocity based on around 100 artificial tracer tests (fluorescent dyes, NaCl salt) carried out in various karst aquifers in Switzerland (Tabular and Folded Jura, Alps (Helvetic realms)) and in various hydrological conditions has been led to, determine the validity of a mean transfer function. The following parameters had been taken into consideration in the variance analysis : geological context, water catchment size, injection site's nature, hydrological conditions, tracing distance and discharge level. Results of this variability study show that mean transfer functions for a water catchment basin do not exist ! No significant difference of the considered parameters is relevant. Nevertheless, mean transfer functions from tracer tests corresponding to a given geological context or to given injection point's nature can be differentiated. The validity of the transfer functions intra-water catchment basin is important and depends principally to the injection sites. At the scale of a water catchment basin, tracer tests are not the single tool used to protect the groundwater : a multiattribute approach has to be applied to assess the vulnerability. In order to outline groundwater protection zones of a water catchment basin an input-response method for tracing-pathway characterizing is not sufficient. An original mutiattribute approach based on a parametric conceptual model of the karst aquifer, the EPIK method has been specificially developed for outlining and rating the water catchment basin talking into account the groundwater sensitivity to all kinds of contaminants. EPIK for Epikarst, Protective cover, Infiltration conditions and Karst network development has been applied on two test-sites in the Swiss Jura (St-Imier's springs water catchment basin in the Folded Jura and the Font, Saivu and Bâme's water catchment basin in the Tabular Jura (Bure)) to assess the vulnerability. The resulting vulnerability maps were the basis for outlining the groundwater protection zones according to the Swiss water and environment regulations. By applying this method on these twi test-sites using a GIS, it appears that outlining karst groundwater protection zones from the multiattribute vulnerability mapping is feasible in a reasonable time invest. If the weighting of key attribute into protection factor appears to be logical, the obtained values may dangerously hide the weakness of the method in a simple index. Although the concept underlying these new vulnerability mapping approach is clear nowadays, futher developments are still needed to appreciate fully its pertinence, specificially regarding the epikarst, the protective cover attributes and the validation of the weighting system that is still problematic. On critical points in a water catchment basin, tracer tests may be carried out. In the framework of hydrological impact assessment, it remains useful to carry out repeated tracer tests, at least three, in various and/or extreme hydrological conditions to define characteristic transfer functions, used to etablish contaminant forecasting. |
| Diplôme : | Docteur des Sciences |
Exemplaires (1)
| Centre | Localisation | Section | Cote | Statut | Disponibilité |
|---|---|---|---|---|---|
| Nancy | ASTER | Ouvrages | DOE 9639 / Environnement | Consultable sur place | Exclu du prêt |
